#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
template<const int MOD> struct modint{
    long long val;
    modint(): val(0) {}
    modint(long long x){
        if(x < 0) val = x % MOD + MOD;
        else val = x % MOD;
    }
    modint(const modint &t){
        val = t.val;
    }
    modint& operator =(const modint m){
        val = m.val;
        return *this;
    }
    modint operator -(){
        return modint(-val);
    }
    modint& operator-=(const modint &m){
        val -= m.val;
        if(val < 0) val += MOD;
        return *this;
    }
    modint& operator+=(const modint &m){
        val += m.val;
        if(val >= MOD) val -= MOD;
        return *this;
    }
    modint& operator*=(const modint &m){
        val *= m.val;
        val %= MOD;
        return *this;
    }
    modint& operator/=(modint m){
        *this *= m.inv();
        return *this;
    }
    modint inv(){
        long long x = 1, y = 0;
        long long a = val, b = MOD;
        while(b != 0){
            long long t = a / b;
            a -= t * b;
            x -= t * y;
            swap(a, b);
            swap(x, y);
        }
        x %= MOD;
        if(x < 0) x += MOD;
        return modint(x);
    }
    modint pow(long long k){
        long long res = 1;
        long long v = val;
        while(k > 0){
            if(k & 1) res = res * v % MOD;
            v = v * v % MOD;
            k >>= 1;
        }
        return modint(res);
    }
    bool operator==(const modint &m){
        return val == m.val;
    }
    modint operator+(const modint &m){
        return modint(*this) += m;
    }
    modint operator-(const modint &m){
        return modint(*this) -= m;
    }
    modint operator*(const modint &m){
        return modint(*this) *= m;
    }
    modint operator/(const modint &m){
        return modint(*this) /= m;
    }
    bool operator!=(const modint &m){
        return modint(*this).val != m.val;
    }
    bool operator!=(const int &m){
        return modint(*this).val != m;
    }
};
const int MOD = 1000000007;
using mint = modint<MOD>;
void dfs(int now, int par, vector<vector<int>>&G, vector<vector<mint>>&dp){
    dp[now].resize(2);
    dp[now][1] += 1;
    for(int to : G[now]){
        if(to == par) continue;
        dfs(to, now, G, dp);
        vector<mint> temp(dp[now].size() + dp[to].size() - 1);
        for(int i = 0; i < (int)dp[now].size(); i++){
            for(int j = 0; j < (int)dp[to].size(); j++){
                temp[i + j] += dp[now][i] * dp[to][j];
            }
        }
        dp[now] = temp;
    }
    dp[now][0] = 1;
}
int main(){
    int N, K;
    cin >> N >> K;
    vector<vector<int>> G(N);
    for(int i = 0; i < N - 1; i++){
        int a, b;
        cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }
    vector<vector<mint>> dp(N);//白が何個あるか
    dfs(0, -1, G, dp);
    cout << dp[0][N - K].val << endl;
}